Disorders of the central retina (known as the macula) such as age-related macular degeneration (ARMD) and diabetic retinopathy are the leading cause of severe visual loss among older adults in the Western world. In their early stages these diseases might cause mild changes in the macula with minimal loss of vision. In some patients the disease can advance to a more visually debilitating stage characterized by the development of abnormal new vessels in the macula, a process known as neovascularization. If left untreated, these abnormal vessels leak plasma leading to edema of the macula and later can bleed causing permanent loss of central vision. If some of these pathological changes are detected in early stages, laser photocoagulation of neovascular nets can slow or prevent the development of advanced disease.
One of the early symptoms of disease progression is distortion of central vision known as Metamorphopsia. Metamorphopsia is a geometric distortion of the central visual field. A patient with metamorphopsia often complains that edges that should be straight (such as the edge of a door or window) instead appear bent in the affected regions of the visual field. As this is an early symptom of disease progression, being able to detect it as early as possible can be critical in the early diagnosis and treatment of these sight threatening conditions.
A common clinical approach for detecting and documenting metamorphopsia is to use an Amsler grid, which is a printed square grid, usually 10 cm wide and 10 cm high, containing equally spaced, parallel horizontal and vertical lines. Typical embodiments of the printed grid include individual 5 mm×5 mm squares of equal area, arranged around a fixation point (such as a dot) at the center of the grid. In use, the grid is held at arm's length, e.g. a distance of about 28-30 cm, while one eye is occluded, and the open eye fixes on the central fixation point. Areas of distortion or wavy lines are then noted by the subject, who may draw a circle around the areas of grid distortion. The subject is usually given a smaller, credit card sized, version of the Amsler grid (known as a pocket Amsler card) so that he or she may self-perform the test at home at regular intervals or whenever he or she suspects changes in vision. The subjects are instructed to immediately report any changes in the severity or distribution of the distortion, as these may indicate progression of the disease that requires immediate treatment.
A need exists in the art for an easy to use, hand-held, portable electronic version of the Amsler test (in all applicable sizes, including the full, pocket-card and any intermediate sizes) that would allow people suffering from diseases that affect the macula to be reminded automatically or remotely of the need to perform the Amsler test, in a simple and cost-conscious way, at a time and place of their choosing, with the ability to record and transmit the results in electronic format, perhaps even tailor the test to their already known clinical condition.
This information could then be sent electronically to a printer, storage and/or another electronic device, making the results available to doctors, physicians, nurses, technicians or other health providers (collectively called clinicians here) to review, asses and determine corrective treatment actions. In addition, the results could be made automatically part of the patients Electronic Medical Records (EMR), or electronically processed to display not only test results, but also test statistics to clinicians.